This invention relates to a rotatable abrading device, and more particularly, to a mechanical device for propelling abrasive materials at abrading velocities against a surface to be treated. Such devices are commonly known as centrifugal blasting machines or abrasive throwing wheels. This invention also relates to an assembly comprised of a blade block, a blade and a locking means for locking the blade in position on the blade block.
Centrifugal blasting machines comprising rotors or wheels having a plurality of blades installed thereon have been known in the art for many years. The blades propel an abrasive material against a work surface. Thus, they are sometimes referred to as throwing blades. Due to the action of the abrasive material on the throwing blades, the blades exhibit considerable wear over a period of time. Attempts have been made to fabricate the blades from abrasion-resistant alloys. In other cases, special blade configuration have been employed to minimize the effects of the abrasive material on the blades.
Notwithstanding these attempts to minimize wear and extend the life of the throwing blades, periodic blade removal and replacement is necessary. This results in a loss of valuable operating time. Furthermore, while the blades must be removable, they must also be held so securely that they will resist the tremendous centrifugal forces exerted on them when the wheel is operating.
Several methods have been proposed for securing the blades in a removable manner to the throwing wheel. One method involves securing the blades to the front side of a wheel disk, usually by means of a bolt or by means of radial grooves in the wheel, frequently of a dove-tail shape. Another method employs two wheel disks that are maintained in spaced-apart relation. Longitudinal narrow edges of the throwing blades are generally inserted into radial grooves arranged in opposing surfaces of the two disks. Auxiliary means, such as bolts, pivotal locking means, eccentrics, set screws, etc. can be employed to secure the blades against radial displacement. Examples of these devices can be found in U.S. Pat. No. 2,819,562, U.S. Pat. No. 3,352,064 and U.S. Pat. No. 3,654,736. Blade replacement is not always easy because the blades "freeze" or become jammed in the grooves.
Another arrangement is shown in U.S. Pat. No. 3,894,360. In this case, the blades are mounted on brackets having an angular cross-section, and the brackets, in turn, are mounted on the throwing wheel. The rear of each blade is provided with a cast-in insert stud, which is adapted for insertion through an opening in the angular bracket. The stud is provided with a slot adapted to receive a clip, which holds the blade in position on the angular bracket. The only securing means in this arrangement is comprised of the stud and the spring clip. Should either the stud or spring clip fail, such as by the blade wearing thin around the area of the stud, the blade will fly off the wheel.
Another arrangement is shown in U.S. Pat. No. 3,867,791, the entire disclosure of which is relied upon and incorporated herein by reference. In this case, the throwing blade is secured to the wheel by means of a blade block, which is mounted on the wheel. Each blade block has a first groove near an inner end of the block and a second groove near an outer end. Each blade includes lugs for insertion in the grooves. There is a centrally disposed impeller that restricts the movement of the blades, particularly in a radial direction. This is accomplished by employing an impeller having a shoulder that contacts the inner end of the blade. While a degree of commercial success has been achieved with this device, the rear of the blade must generally be machined in the area where it contacts the impeller. This adds to the cost of the blades. Additionally, it has been found to be rather difficult to cast the blade of the type disclosed in the patent because of its large cross-sectional area.
In short, there exists a need in the art for improved means for securing the throwing blades to the wheel of a centrifugal blasting machine. The throwing blades must be securely mounted on the throwing disk to prevent movement of the blades, especially in a radial direction. The blades must be easily removed and replaced without the need for special tools. Preferably, the blades should not be susceptible to "freezing" or jamming in position, as is frequently encountered when the blades are installed in grooves on the disk of the abrasive blasting machine. When the blade is installed in the centrifugal blasting machine, it should be possible to replace the blade without removing the internal parts of the blast machine, such as the impeller or control cage conventionally found in such machines. The means used for locking the blade in position should be suitable for use with any length and width of blade. The assembly should not require machining and close tolerances characteristic of prior art devices. For commercial reasons, the blade and blade block assembly should be adapted to fit centrifugal blasting machines now on the market.